Portable refrigerant recovery machines are used to transfer refrigerant from a refrigerant containing device, such as an air-conditioning unit for a home to a refrigerant storage tank. Many recovery machines are designed with a single cylinder, “oil less” compressor and include a pressurized crank case, which increases pressure during the intake stroke, thereby storing potential energy in the compressed refrigerant. As the piston begins the compression stroke, the stored potential energy in the compressor refrigerant in the crank case is used to help push the piston up the stroke and compress the refrigerant in the cylinder against the head pressure. This “assist” reduces the required load on the motor since 180 degrees of the motor's revolution is used to store energy in the compressed refrigerant crankcase when it would otherwise be wasted by merely moving the piston down the cylinder. A disadvantage to this arrangement is that the refrigerant will remove the lubrication in the moving components in the crankcase, which are typically ball bearings, leading to accelerated failure of the compressor. Further, one cylinder compressor can only move a certain volume of refrigerant once during a single motor revolution.
Accordingly, it is desirable to provide refrigerant recovery machine that does not require a pressurized crankcase and has a two cylinder compressor to move more refrigerant during a single motor rotation.